1. Field of the Invention
The present invention relates generally to a linear scale incorporating a magnetic scale, an optical scale or the like. More particularly, the invention relates to a linear scale unit which can be easily assembled and easily mounted on a machine tool or other devise to be monitored.
2. Description of the Prior Art
Magnetic scales and optical scales, among others, have been used for numerical machine tool control. Conventional scale elements have been fixedly mounted on the machine tool by means of a base. This causes problems during maintenance and replacement of the linear scale. For instance, the alignment of conventional linear scales must be adjusted each time the scale is detached from the machine tool. Alignment adjustment is conventionally performed by means of a pick-tester, adjusting shims and so forth and is relatively time-consuming for truly accurate adjustment of the alignment. Furthermore, conventional scales require delicate adjustment when installing the scale unit on the machine tool using spacers to compensate for inevitable distortions or slight bends in the scale channel incurred during manufacture.
Furthermore, with conventional scales, additional problems are encountered in fitting a head assembly of the scale unit onto a fitting bracket of the machine tool. The conventional technique for fitting the head assembly onto the fitting bracket is to adjust the vertical height of a head carrier relative to the fitting bracket by means of a spacer. The range of adjustment of the head assembly with respect to the fitting bracket by means of the spacer is very limited. This requires adjustment of the height of the fitting bracket at the user's end.